The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This disclosure relates to methods and apparatuses for pressure testing tubular bodies, for example casing or tubing strings installed in subterranean wells.
During the construction of subterranean wells, it is common, during and after drilling, to place a tubular body in the wellbore. The tubular body may comprise drillpipe, casing, liner, coiled tubing or combinations thereof. The purpose of the tubular body is to act as a conduit through which desirable fluids from the well may travel and be collected. The tubular body is normally secured in the well by a cement sheath. The cement sheath provides mechanical support and hydraulic isolation between the zones or layers that the well penetrates. The latter function is important because it prevents hydraulic communication between zones that may result in contamination. For example, the cement sheath blocks fluids from oil or gas zones from entering the water table and polluting drinking water. In addition, to optimize a well's production efficiency, it may be desirable to isolate, for example, a gas-producing zone from an oil-producing zone.
Conventionally, production tubing is placed inside the casing in the vicinity of the zone from which hydrocarbons are extracted. The production tubing is generally hydraulically isolated by a packer that seals the production tubing/casing annulus.
A tubingless completion is one in which relatively small-diameter production casing is used to produce the well without the need for production tubing. The advantage of such completions is economic in that it may save five to six days rig time. Operations such as running and cementing liner, wellbore cleanup and packer setting procedures are eliminated.
After running the production casing into the wellbore, and prior to performing the cement job, it may be necessary to perform a pressure test of the casing string. There are three common methods by which this may be accomplished.
A plug may be run down the casing via slickline, after which the fluid between the surface and the plug is pressurized to the desired level. After the test, the plug is pulled out of the hole. The disadvantage of this technique is that the portion of casing below the plug is not tested.
A calibration plug may be used. In this method a first plug is circulated down the casing and it lands on a landing collar. The string can then be pressure tested. This is simple and reliable; however, to reestablish communication between the casing interior and the annulus, the pressure inside the string must be increased to a higher level to open a port (usually a burst disk). This operation may also be costly because of the rig time necessary to circulate the plug downhole.
A ball may be pumped. A ball seat is set in the casing string. When the ball lands, the string can be pressure tested. However, the ball must be sheared out at a higher pressure after the test, possibly compromising casing integrity.